Short-range automobile wireless communication device

ABSTRACT

In a short-range on-vehicle radio communication system having in-car radio communication function, a two-way transmission antenna ( 9   a ) for radio communication is arranged at a panel portion ( 8   c ) outside a sheet metal chassis ( 8   b ) of a car navigation unit ( 8 ). As a result, the communication area becomes large, signals including those from a cellular phone ( 2   b ) of low radio communication output power are easily received, and it is possible to save manufacturing cost.

FIELD OF THE INVENTION

[0001] The present invention relates to an arrangement of a two-waytransmission antenna for radio communication in a short-range on-vehicleradio communication system having in-car radio communication function.

BACKGROUND ART

[0002]FIG. 15 is a block diagram of a conventional hands-free system. Acellular phone base station 1 and a cellular phone 2 are connected via apublic radio communication line. Signals are transmitted and receivedbetween the cellular phone 2 and a hands-free unit 3 via a connector 2Cprepared in the cellular phone 2. A microphone 4 and a speaker 5 areconnected to the hands-free unit 3. Telephone signals gathered by themicrophone 4 arranged in a vehicle are transmitted to the cellular phonebase station 1 via the hands-free unit 3 and the cellular phone 2. Then,the telephone signals are transmitted from the cellular phone basestation 1 to a person on the other end of a so-called public telephoneline. On the other hand, telephone signals from the person on the otherend of the line are transmitted to the hands-free unit 3 through thereverse path. The speaker 5 reproduces the telephone signals from theperson on the other end of the line inputted to the hands-free unit 3.The cellular phone 2, the hands-free unit 3, the microphone 4 and thespeaker 5 are arranged in the vehicle 6.

[0003] The hands-free system shown in FIG. 15 has a disadvantage in theaspect that it is necessary to connect the connector 2C of the cellularphone 2 every time a cellular phone user gets on the vehicle. Moreover,it is also necessary to disconnect the connector 2C when the user getsout of the vehicle. Furthermore, when the connector 2C is not connected,the connector 2C with cable should be put away to avoid the car roomfrom looking not neat.

[0004]FIG. 16 is a block diagram of another conventional hands-freesystem, which overcomes the mentioned disadvantage of the hands-freesystem of FIG. 15. The hands-free system shown in FIG. 16 is disclosed,for example, in the Japanese Patent Publication (unexamined) No.276261/1998 titled “Radio Communication System”. A difference from thehands-free system of FIG. 15 consists in that the, instead of the cablesystem, the cellular phone 2 a and the hands-free unit 3 a are connectedby a radio system (or an infrared system). Flow of the telephone signalsis the same as in the case of FIG. 15, and further description thereofis omitted herein. In another known system disclosed in the JapanesePatent Publication (unexamined) No. 331064/1999 titled “Hands-freeTelephone System”, a radio (FM) circuit portion built in the cellularphone 2 a body is formed into a radio module 7 and is arranged at aconnector portion of the cellular phone 2 a.

[0005] The disadvantages of connecting and disconnecting the connectorof the cellular phone 2 a and looking not neat are overcome by using theradio system (or the infrared system) in connecting the cellular phone 2a and the hands-free unit 3 a. In the case of the infrared system, it isnecessary that infrared transmitting and receiving sections of thecellular phone 2 a and the hands-free unit 3 a are arranged opposite toeach other. On the contrary, in the case of the radio system, it is notnecessary that the transmitting and receiving sections of the cellularphone 2 a and the hands-free unit 3 a are arranged opposite to eachother.

[0006] As a short-range radio communication system of such type,Bluetooth SIG has proposed a “Bluetooth” system. (BLUETOOTH is aregistered trademark of Telefonaktiebolaget L M Ericsson, Sweden.)

[0007] The mentioned system has the following characteristics:

[0008] (1) Cordless communication between one apparatus and another isachieved.

[0009] (2) Radio circuit of this system is applicable to a variety ofapparatuses such as personal computers, printers, cellular phones,personal digital assistants, etc.

[0010] (3) The global standard is adopted.

[0011] (4) Both voice and data communication can be transmitted andreceived.

[0012] (5) A frequency band of 2.4 GHz called an ISM band is adopted.

[0013] (6) It is not necessary to arrange the communication apparatusesopposite to each other unlike those in the infrared communication.

[0014] (7) Communication between apparatuses is available in the form ofnot only 1 to 1 like the infrared communication but also 1 to 7(maximum).

[0015] (8) It is possible to choose any output power convenient for eachapparatus because there are following three types of outputs:

[0016] Class 1: 100 mW (+20 dBm) max;

[0017] Class 2: 2.5 mW (+4 dBm) max; and

[0018] Class 3: 1 mW (0 dBm) max.

[0019] In choosing one output power among the three types described inthe foregoing characteristic (8) of the system, Class 3 of the smallestpower consumption (i.e., the battery life is long) for a portable devicesuch as cellular phone. It is preferable to adopt Class 1 from theviewpoint of giving an importance to a communication area such as homemodem station where communication with each room is available on thepower-saving basis.

[0020] Supposing that a radio communication is conducted using acellular phone having a small radio communication output power functionlike in the foregoing system with a cellular phone brought into avehicle, it is possible to utilize this radio communication enjoying thefollowing advantages:

[0021] (1) Hands-free telephone

[0022] {circle over (1)} Cordless and hands-free telephone is availableeven when the cellular phone is put in a bag, on a rear seat, or thelike.

[0023] {circle over (2)} This contributes to safe driving.

[0024] (2) Information and communication display

[0025] {circle over (1)} Information provided by an IT-adapted cellularphone of a mobile communication company is displayed on a map display ofa car navigation unit. The information is enlarged on the display andeasy to see.

[0026] {circle over (2)} Plural persons in the vehicle can see thedisplay at the same time.

[0027] {circle over (3)} This contributes to safe driving.

[0028] Now, environment of the radio communication is described below.

[0029] (1) A power-saving type is adopted as the radio output power ofthe cellular phone in most cases.

[0030] {circle over (1)} In the case of power-saving output power, it isconsidered that communication is available within a distance of severalmeters.

[0031] (2) In the cases of the foregoing hands-free telephone (1) andinformation and communication display (2), a radio communication circuitis built in a car navigation unit in most cases.

[0032] {circle over (1)} As the car navigation unit is composed of asheet metal chassis, a radio communication antenna is arranged insidethe sheet metal chassis of the car navigation unit, and thereforesensitivity is low.

[0033] {circle over (2)} The car navigation unit is arranged at any ofvarious places such as center console, under side of seat, and trunk.

[0034] {circle over (3)} In the case of arranging the car navigationunit in the trunk, to be free from outside influence such as “pressure”,“waterdrop”, and the like from loaded cargo, the unit incorporating thecommunication antenna of the car navigation may be further covered witha sheet metal when required.

[0035] Accordingly, an object of the invention is to provide ashort-range on-vehicle radio communication system having in-car radiocommunication function, capable of widening the communication area sothat any signal from a cellular phone of low radio communication outputpower as described above may be easily received.

DISCLOSURE OF INVENTION

[0036] The invention provides a short-range on-vehicle radiocommunication system having an in-car radio communication function, inwhich a two-way transmission antenna for radio communication is arrangedoutside a sheet metal chassis of a main body. As a result of employingsuch an arrangement, communication area becomes larger and any signalfrom a cellular phone of low radio communication output power might beeasily received.

[0037] The invention is applied to a car navigation unit, and thetwo-way transmission antenna for radio communication is arranged at apanel portion outside the sheet metal chassis of the car navigationunit. As a result of employing such an arrangement, communication areabecomes broader, any signal from a cellular phone of low radiocommunication output power might be easily received, and it is furtherpossible to save the manufacturing cost.

[0038] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich the two-way transmission antenna for radio communication isarranged outside the main body. As a result of employing such anarrangement, a stable and large communication area is securedirrespective of the place of locating the short-range on-vehicle radiocommunication system main body, and any signal from a cellular phone oflow radio communication output power might be easily received.

[0039] The invention provides the system of the short-range radiocommunication of which radio communication output power is small, whichis applied to the car navigation unit. As a result of employing such anarrangement, the problem of communication antenna being low insensitivity is solved, and any signal from a cellular phone of low radiocommunication output power of several meters in communication availabledistance is might be easily received.

[0040] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich the two-way transmission antenna for radio communication isarranged at a ceiling in a car room. As a result of employing such anarrangement, influence due to the place where the person to communicateto (i.e., the cellular phone) is located in the car room, is less.Furthermore, difference in distance between each place where the mainbody of the short-range on-vehicle radio communication system is locatedin the vehicle and the two-way transmission antenna for radiocommunication is reduced, and therefore fluctuation in loss caused bycable length is restrained.

[0041] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich the two-way transmission antenna for radio communication isarranged in an interior light module on the ceiling in the car room, ona surface of the module, or around the module. As a result of employingsuch an arrangement, the two-way transmission antenna for radiocommunication is out of sight, and wiring can be performed together withwiring for the interior light. The antenna can be arranged on theceiling together with the interior light module. Further, the influencedue to the place where the person to communicate to (i.e., the cellularphone) is located in the car room is reduced. Difference in distancebetween each place where the main body of the short-range on-vehicleradio communication system is arranged in the vehicle and the two-waytransmission antenna for radio communication is less, and thereforefluctuation in loss caused by the cable length is restrained.

[0042] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich the two-way transmission antenna for radio communication isarranged on the front seat side. As a result of employing such anarrangement, the two-way transmission antenna for radio communication islocated in the vicinity of the cellular phone brought into the vehicleby a driver who uses the hands-free telephone in most cases, whichincreases reliability in transmitting and receiving through the radiocommunication.

[0043] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich the two-way transmission antenna for radio communication isarranged on an outer circumference of the main body. As a result ofemploying such an arrangement, the antenna cable is shortened and lossdue to cable length is less. Further the antenna mounting work becomeseasy.

[0044] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich plural two-way transmission antennas for radio communication arearranged outside the sheet metal chassis of the main body in thevehicle. As a result of employing such an arrangement, thecommunication-available area becomes highly reliable, which enablesdevelopment for large-sized vehicles such as buses.

[0045] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich among the plural two-way transmission antennas for radiocommunication, one is arranged at a front portion inside the vehicle andanother one is arranged at a rear portion inside the vehicle.

[0046] The invention provides the short-range on-vehicle radiocommunication system having in-car radio communication function, inwhich among the plural two-way transmission antennas for radiocommunication, one is arranged at a panel portion outside the sheetmetal chassis and another one is arranged outside the main body.

[0047] Furthermore, the invention provides the short-range on-vehicleradio communication system having in-car radio communication function,in which an antenna output of the highest reception level is selectedamong the plural two-way transmission antennas for radio communication.As a result of employing such an arrangement, when the person tocommunicate to uses a communication apparatus of small communicationoutput power, the communication is secured even when the person tocommunicate to moves. This enables development for large-sized vehiclessuch as buses.

BRIEF DESCRIPTION OF DRAWINGS

[0048]FIG. 1 is a schematic diagram showing an arrangement according toEmbodiment 1 of the invention.

[0049]FIG. 2 is a schematic diagram showing an arrangement according toEmbodiment 2 of the invention.

[0050]FIG. 3 is a schematic view showing an arrangement according toEmbodiment 3 of the invention.

[0051]FIG. 4 is a schematic view showing an arrangement according toEmbodiment 4 of the invention.

[0052]FIG. 5 is a schematic view showing an arrangement according toEmbodiment 5 of the invention.

[0053]FIG. 6 and FIG. 7 are a schematic view and a perspective viewrespectively showing an arrangement according to Embodiment 6 of theinvention.

[0054]FIG. 8 is a perspective view showing an arrangement according toEmbodiment 7 of the invention.

[0055]FIG. 9 is a perspective view showing an arrangement according toEmbodiment 8 of the invention.

[0056]FIG. 10 is a schematic view showing an arrangement according toEmbodiment 9 of the invention.

[0057]FIG. 11 is a schematic view showing an arrangement according toEmbodiment 10 of the invention.

[0058]FIG. 12 is schematic view showing an arrangement according toEmbodiment 11 of the invention.

[0059]FIG. 13 is a schematic view showing an arrangement according toEmbodiment 12 of the invention.

[0060]FIG. 14 is a block diagram showing Embodiment 13 of the invention,and is a block diagram of an antenna output selection circuit showing anessential part of Embodiment 12.

[0061]FIG. 15 is a block diagram of a conventional hands-free system.

[0062]FIG. 16 is a block diagram of another conventional hands-freesystem.

BEST MODE FOR CARRYING OUT THE INVENTION

[0063] In the case of performing a radio communication between acellular phone and an on-vehicle radio communication system (a carnavigation unit), a power-saving type output power is adopted as theradio output power of the cellular phone in most cases.

[0064] On the other hand, the on-vehicle radio communication system (thecar navigation unit) is covered with a sheet metal chassis except for apanel face.

[0065] Embodiment 1.

[0066] Taking account of the foregoing conditions, Embodiment 1 of theinvention is hereinafter described with reference to FIG. 1. FIG. 1 is aschematic diagram showing an arrangement according to Embodiment 1 ofthe invention. It is supposed herein that a short-range radiocommunication is performed between a cellular phone 2 b and a carnavigation unit 8 (a short-range on-vehicle radio communication system)each having short-range radio communication function. In this case, if atwo-way transmission antenna 9 a for short-range radio communication inthe can navigation unit 8 is arranged inside a sheet metal chassisportion 8 b, radiation pattern characteristic of the two-waytransmission antenna 9 a for radio communication is restricted, and anarea where communication is available becomes narrow. In order to relaxthe restriction on the radiation pattern characteristic of the two-waytransmission antenna 9 a for radio communication, the two-waytransmission antenna 9 a for radio communication is arranged outside thesheet metal chassis portion 8 b of the can navigation unit 8, i.e., at apanel portion 8 c.

[0067] As a result, the communication area becomes large, and thisimproves reception of signals including those from the cellular phone 2b of low short-range radio communication output power. It is possible tosave the manufacturing cost by arranging the two-way transmissionantenna 9 a for radio communication at the panel portion 8 c outside thesheet metal chassis portion 8 b of the car navigation unit 8.

[0068] The car navigation unit 8 has hands-free function, and to whichthe microphone 4 and the speaker 5 is connected. The cellular phone 2 b,the car navigation unit 8, the microphone 4, and the speaker 5 are alllocated in the vehicle 6. Telephone signals gathered by the microphone 4arranged in the vehicle 6 are transmitted to the cellular phone basestation 1 via the car navigation unit 8 and the cellular phone 2 b. Onthe other hand, telephone signals from the person on the other end ofthe line are transmitted to the car navigation unit 8 through thereverse path. The speaker 5 reproduces telephone signals of the personon the other end of the line inputted to the car navigation unit 8. Itis a matter of course that the system shown in FIG. 1 is also applicableto a case of displaying data other than the telephone signals from thecellular phone 2 b on the map display (not shown) for the car navigationunit 8, and to a case of transmitting data other than the telephonesignals from the car navigation unit 8 to the cellular phone 2 b.

[0069] Embodiment 2.

[0070]FIG. 2 is a schematic diagram showing an arrangement according toEmbodiment 2 of the invention. In this Embodiment 2, the two-waytransmission antenna 9 a for short-range radio communication of the cannavigation unit 8 a is arranged outside the car navigation unit 8 a.This two-way transmission antenna 9 a for short-range radiocommunication is covered with a resin case or the like that does notrestrict the radiation pattern characteristic of the antenna 9 a.

[0071] As a result of employing such arrangement, it is obvious that thecommunication area is not restricted by the sheet metal chassis 8 b andthe short-range radio communication environment is further improved.Furthermore even in the case that the car navigation unit 8 a isarranged at a place where the radio environment is not desirable, it ispossible to achieve a favorable short-range radio communication with thecellular phone 2 b. Particularly in the case that the car navigationunit 8 a is arranged in the trunk, or even in the case that the unit 8 ais covered with a protective sheet metal for protection from “externalpressure” “water drop”, arranging the two-way transmission antenna forshort-range radio communication outside the car navigation unit 8 amakes it possible to stably secure the communication-available areairrespective of the place where the car navigation unit 8 a main body isarranged.

[0072] Embodiment 3.

[0073]FIG. 3 is a schematic view showing an arrangement according toEmbodiment 3 of the invention. FIG. 3 shows Example 1 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 1 showing the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged at the ceiling in the car room (Place A). As aresult, the radio environment between the two-way transmission antenna 9a for short-range radio communication and the cellular phone 2 b locatedat any of points α, β, γ, and δ in the car room is good in the samemanner. Influence due to the place of the person to talk to (i.e., placeof the cellular phone) in the car room is minimum.

[0074] In the case that the car navigation unit 8 a is arranged at anyof the points a, b, and c in the vehicle, the distance between thetwo-way transmission antenna 9 a for short-range radio communication andthe car navigation unit 8 a is almost equal, and fluctuation in losscaused by a cable length is restrained. Furthermore, even in the casethat the car navigation unit 8 a is arranged in the trunk and the unitis covered with a protective sheet metal 10 for protection from“external pressure” “water drop”, it is possible to keep radioenvironment good between the two-way transmission antenna 9 a forshort-range radio communication and the cellular phone 2 b.

[0075] Embodiment 4.

[0076]FIG. 4 is a schematic view showing an arrangement according toEmbodiment 4 of the invention. FIG. 4 shows Example 2 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 2 showing the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication isarranged, the antenna 9 a is arranged in an interior light module (PlaceB) in the car room, on a surface of the module or around the module. Asa result, the following advantages are obtained in addition to thosedescribed in Embodiment 3.

[0077] First, in the case of arranging the two-way transmission antenna9 a for short-range radio communication in the interior light module,the two-way transmission antenna 9 a for short-range radio communicationis out of sight, and the car room looks very neat. Furthermore, thetwo-way transmission antenna 9 a for short-range radio communication iswired together with wiring of the interior light module, thereby workefficiency being improved.

[0078] In the case of arranging the two-way transmission antenna 9 a forshort-range radio communication on the surface of the interior lightmodule or in the vicinity thereof, not only the two-way transmissionantenna 9 a for short-range radio communication is wired together withwiring of the interior light module, but also the two-way transmissionantenna 9 a for short-range radio communication and the interior lightmodule can be installed at the same time, thereby work efficiency beingimproved.

[0079] In the foregoing description, the antenna is arranged in theinterior light module in the car room, on the surface of the module oraround the module. The same advantages as in the interior light moduleare also obtained by arranging the two-way transmission antenna 9 a forshort-range radio communication integrally with a rearview mirror (roommirror) in the car room or by arranging the two-way transmission antenna9 a for short-range radio communication around the rearview mirror.

[0080] In other words, in the case that the antenna 9 a is arrangedintegrally with the rearview mirror (room mirror), the car room looksneat. In the case that the antenna 9 a is arranged around the rearviewmirror (room mirror), a mounting member for mounting the rearview mirror(room mirror) and a mounting member for mounting the two-waytransmission antenna. 9 a for short-range radio communication can becombined, and the rearview mirror (room mirror) and the two-waytransmission antenna 9 a for short-range radio communication can bearranged at the same time, thereby work efficiency being improved.

[0081] Embodiment 5.

[0082]FIG. 5 is a schematic view showing an arrangement according toEmbodiment 5 of the invention. FIG. 5 shows Example 3 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 3 showing the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged on the front seat side in the car room (Place C:the two-way transmission antenna 9 a for short-range radio communicationis arranged under the assistant driver's seat in FIG. 5). As a result,there is a possibility that the antenna 9 a is located in the vicinityof the cellular phone brought into the vehicle by the driver who issupposed to use the mentioned hands-free telephone in most cases,thereby reliability on transmitting and receiving in radio communicationbeing improved.

[0083] Embodiment 6.

[0084]FIG. 6 is a schematic view showing an arrangement according toEmbodiment 6 of the invention. FIG. 6 shows Example 4 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 4 showing the aspect of arranging the two-waytransmission antenna 9 a for short-range radio, the antenna 9 a isarranged on a surface of a dashboard in the car room, inside thedashboard or around the dashboard (Place D). The portion indicated bythe half-tone dot meshing in FIG. 7 shows the Place D in an image ofactual vehicle.

[0085] As a result, in the case that the car navigation unit 8 a isarranged either at a point a (center console) or at a point b (under thefront seat) in the vehicle, the distance between the two-waytransmission antenna 9 a for short-range radio communication and the carnavigation unit 8 a is shorter than that in the foregoing Embodiment 3or 4, and loss caused by the cable length is reduced. Further, mountingthe two-way transmission antenna 9 a for short-range radio communicationis easier than that in the foregoing Embodiment 3 or 4.

[0086] Furthermore, arranging the cellular phone 2 b either at the pointγ or at the point δ in the car room does not cause any significantdeterioration in radio environment between the two-way transmissionantenna 9 a for short-range radio communication and the cellular phone 2b.

[0087] Embodiment 7.

[0088]FIG. 8 is a perspective view showing an arrangement according toEmbodiment 7 of the invention. FIG. 8 shows Example 5 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 5 showing the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged on a surface of the center console or floorconsole (the portion indicated by half-tone dot meshing in FIG. 8) inthe car room, inside the console or around the console. As a result,there is a possibility that the antenna 9 a is located in the vicinityof the cellular phone brought into the vehicle by the driver who issupposed to use the mentioned hands-free telephone in most cases,thereby reliability on transmitting and receiving in radio communicationbeing improved.

[0089] Consequently, in the case that the car navigation unit 8 a isarranged either at a point a (center console) or at a point b (under thefront seat) in the vehicle, particularly at the point a (the centerconsole), the distance between the two-way transmission antenna 9 a forshort-range radio communication and the car navigation unit 8 a isshorter than that in the foregoing Embodiment 3 or 4, and loss caused bythe cable length is reduced. Further, mounting the two-way transmissionantenna 9 a for short-range radio communication is easier than in theforegoing Embodiment 3 or 4.

[0090] Embodiment 8.

[0091]FIG. 9 is a perspective view showing an arrangement according toEmbodiment 8 of the invention. Numeral 2 d is a cellular phone holderarranged at the place indicated by the arrow. FIG. 9 shows Example 6 ofthe aspect of arranging the two-way transmission antenna 9 a forshort-range radio communication of the car navigation unit 8 a outsidethe car navigation unit 8 a. In this Example 6 showing the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication, the antenna 9 a is arranged in the vicinity of thecellular phone holder in the car room (the portion indicated byhalf-tone dot meshing in FIG. 9). As a result, the antenna 9 a islocated in the vicinity of the cellular phone brought into the vehicle,thereby reliability on transmitting and receiving in radio communicationbeing improved.

[0092] Consequently, in the case that the car navigation unit 8 a isarranged either at a point a (center console) or at a point b (under thefront seat) in the vehicle, particularly at the point a (the centerconsole), the distance between the two-way transmission antenna 9 a forshort-range radio communication and the car navigation unit 8 a isshorter than that in the foregoing Embodiment 3, 4 or 6, and loss causedby the cable length is reduced. Further, mounting the two-waytransmission antenna 9 a for short-range radio communication is easierthan in the foregoing Embodiment 3 or 4.

[0093] Embodiment 9.

[0094]FIG. 10 is a schematic view showing an arrangement according toEmbodiment 9 of the invention. FIG. 10 shows Example 7 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 7 of the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged on a surface of a rear tray in the car room,inside the rear tray or around the rear tray (Place E). As a result, inthe case that the car navigation unit 8 a is arranged at a point c inthe vehicle, the distance between the two-way transmission antenna 9 afor short-range radio communication and the car navigation unit 8 a isshorter than in Embodiment 3 or 4, and the loss caused by the cablelength is reduced. Further, mounting two-way transmission antenna 9 afor short-range radio communication is easier than in the foregoingEmbodiment 3 or 4.

[0095] Furthermore, arranging the cellular phone 2 b either at the pointα or at the point β does not cause any significant deterioration inradio environment between the two-way transmission antenna 9 a forshort-range radio communication and the cellular phone 2 b.

[0096] Embodiment 10.

[0097]FIG. 11 is a schematic view showing an arrangement according toEmbodiment 10 of the invention. FIG. 11 shows Example 8 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 8 of the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged in the trunk of the vehicle. (i.e., Place F: thetwo-way transmission antenna 9 a for short-range radio communication isarranged on the rear side of the rear tray in FIG. 11). As a result, inthe case that the cellular phone is arranged in a bag accommodated inthe trunk, the antenna 9 a is located in the vicinity of the cellularphone, thereby reliability on transmitting and receiving in radiocommunication being improved.

[0098] Further, in the case that the car navigation unit 8 a is arrangedin the trunk as shown in FIG. 11, the distance between the carnavigation unit 8 a and the two-way transmission antenna 9 a forshort-range radio communication becomes shorter. Thus, loss caused bythe antenna cable is reduced, thereby efficiency in mounting work beingimproved. When the driver makes hands-free telephone talk using thecellular phone, it is obvious that the hands-free telephone talk isachieved just by connecting the microphone for the driver arranged inthe vicinity of the driver's seat and the speaker for reproducing thevoice of the person on the other end of the line to the car navigationunit 8 a arranged in the trunk.

[0099] Embodiment 11.

[0100]FIG. 12 is a schematic view showing an arrangement according toEmbodiment 11 of the invention. FIG. 12 shows Example 9 of the aspect ofarranging the two-way transmission antenna 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 9 of the aspect of arranging the two-waytransmission antenna 9 a for short-range radio communication, theantenna 9 a is arranged on the outer circumference of the car navigationunit 8 a (Place G). In this Embodiment 11, the car navigation unit 8 abody is arranged under the front seat. As a result, the distance betweenthe two-way transmission antenna 9 a for short-range radio communicationand the car navigation unit 8 a becomes extremely short, loss caused bythe cable length is extremely small, and mounting work is easy.

[0101] Furthermore, even in the case that the cellular phone 2 b isarranged at any of the points α, β, γ and δ, the radio environmentbetween the two-way transmission antenna 9 a for short-range radiocommunication and the cellular phone 2 b is improved as compared withthe panel portion of built-in antenna type described in the foregoingEmbodiment 1.

[0102] Embodiment 12.

[0103]FIG. 13 is a schematic view showing an arrangement according toEmbodiment 12 of the invention. FIG. 13 shows Example 10 of the aspectof arranging the two-way transmission antennas 9 a for short-range radiocommunication of the car navigation unit 8 a outside the car navigationunit 8 a. In this Example 10 of the aspect of arranging the two-waytransmission antennas 9 a for short-range radio communication, pluraltwo-way transmission antennas 9 a for short-range radio communicationare arranged (at Places D and H). In the drawing, Place D is located onthe dashboard described in Embodiment 6, and Place H is located on therear side of the rear tray described in Embodiment 9.

[0104] As a result, in the case that the cellular phone 2 b is locatedat any of the points α, β, γ, and δ in the car room, a signal of thetwo-way transmission antenna 9 a for short-range radio communication ofPlace D is adopted, and in the case that the cellular phone 2 b islocated at a point ε in the trunk (in a bag in this case), a signal ofthe two-way transmission antenna 9 a for short-range radio communicationof Place H is adopted, thus the communication-available space for thecellular phone 2 b becomes large. This further increases reliability onthe communication-available area. This Embodiment 12 is particularlyeffective when the short-range radio communication system is built in alarge-sized vehicle.

[0105] In the foregoing description, the plural two-way transmissionantennas 9 a for short-range radio communication are arranged, and theantennas 9 a are arranged at the front and the rear sides of thevehicle. As another Example 1 of arranging the plural two-waytransmission antennas 9 a for short-range radio communication, it ispreferable that at least one of the plural two-way transmission antennas9 a for short-range radio communication is arranged on the right side ofthe longitudinal center line of the vehicle, and at least another one ofthem is arranged on the left side of the longitudinal center line of thevehicle. As a result of employing such an arrangement, it is possible toreduce influence of any obstacle that shuts out in the longitudinaldirection of the vehicle such as backrest of seat or human body in thevehicle.

[0106] As a further Example 2 of arranging the plural two-waytransmission antennas 9 a for short-range radio communication, it ispreferable that at least one of the plural two-way transmission antennas9 a for short-range radio communication is arranged on the right side ofthe seating center line of the driver's seat, and at least another oneof them is arranged on the left side of the seating center line of thedriver's seat. As a result of employing such an arrangement, it ispossible to greatly reduce influence of the human body of the driver whouses most frequently the system of the invention such as hands-freetelephone talk system. The mentioned two-way transmission antennas 9 afor short-range radio communication arranged in this manner does notcause any significant deterioration in short-range radio communicationenvironment at any other place than the driver's seat.

[0107] As a further Example 3 of arranging the plural two-waytransmission antennas 9 a for short-range radio communication, it ispreferable that at least one of the plural two-way transmission antennas9 a for short-range radio communication is arranged on the front side ofthe seating center line of the driver's seat, and at least another oneof them is arranged on the rear side of the seating center line of thedriver's seat. As a result of employing such an arrangement, it ispossible to greatly reduce influence of the human body of the driver whouses most frequently the system of the invention such as hands-freetelephone talk system. The two-way transmission antennas 9 a forshort-range radio communication arranged in this manner does not causeany significant deterioration in short-range radio communicationenvironment even in any other place than the driver's seat.

[0108] As a further Example 4 of arranging the plural two-waytransmission antennas 9 a for short-range radio communication, it ispreferable that at least one of the plural two-way transmission antennas9 a for short-range radio communication is “arranged at the panelportion 8 c of the short-range on-vehicle radio communication system(the car navigation unit 8)” described in the foregoing Embodiment 1,and at least another one of them is arranged at a place away from theshort-range on-vehicle radio communication system. As a result ofemploying such an arrangement, only one of the two-way transmissionantennas 9 a for short-range radio communication is arranged outside theshort-range on-vehicle radio communication system, and therefore themounting work is easy. The two-way transmission antennas 9 a forshort-range radio communication arranged in this manner obviouslyimproves the short-range radio communication environment as comparedwith the two-way transmission antenna 9 a for short-range radiocommunication arranged only at the panel portion 8 c of the short-rangeon-vehicle radio communication system (the car navigation unit 8) asdescribed in the foregoing

[0109] Embodiment 1.

[0110] As a further Example 5 of arranging the plural two-waytransmission antennas 9 a for short-range radio communication, it ispreferable that at least one of the plural two-way transmission antennas9 a for short-range radio communication is “arranged on the outercircumference of the short-range on-vehicle radio communication system(the car navigation unit 8)” described in the foregoing Embodiment 11,and at least another one of them is arranged at a place away from theshort-range on-vehicle radio communication system. As a result ofemploying such an arrangement, only one of the two-way transmissionantennas 9 a for short-range radio communication is arranged outside theshort-range on-vehicle radio communication system, and the mounting workis easy. The two-way transmission antennas 9 a for short-range radiocommunication arranged in this manner obviously improves the short-rangeradio communication environment as compared with the two-waytransmission antenna 9 a for short-range radio communication arrangedonly on the outer circumference of the short-range on-vehicle radiocommunication system (the car navigation unit 8) as described in theforegoing Embodiment 11.

[0111] Embodiment 13

[0112]FIG. 14 is a block diagram of an antenna output selective circuitshowing an essential part of Embodiment 13 of the invention. ThisEmbodiment 13 is an example in which two two-way transmission antennasfor radio communication are used, and in which connection is made to theradio communication two-way transmission antenna output of whichreception level is higher. In FIG. 14, numeral 8 a is the car navigationunit having a radio communication function, and numerals 9 a-1 and 9 a-2are the two-way transmission antennas for radio communication arrangedoutside the body of the car navigation unit 8 a. Numerals 30-1 and 30-2are duplexers for switching whether to receive reception signals fromthe two-way transmission antennas 9 a-1 and. 9 a-2 for radiocommunication or transmit transmission signals to the two-waytransmission antennas 9 a-1 and 9 a-2 for radio communication. Numerals11-1 and 11-2 are band-pass filters for passing frequency bands of thereception signals received by the two-way transmission antennas 9 a-1and 9 a-2 for radio communication. Numerals 12-1 and 12-2 are low-noiseamplifiers for amplifying the reception signals that have passed throughthe band-pass filters 11-1 and 11-2. Numeral 13 is a level comparatorfor comparing a level of the reception signal of the two-waytransmission antenna 9 a-1 for radio communication and a level of thereception signal of the two-way transmission antenna 9 a-2 for radiocommunication, and numerals 14-1 and 14-2 are antenna switches forswitching the connection to either of the two-way transmission antennas9 a-1 and 9 a-2 for radio communication. Numeral 15 is an A/D converterfor converting a received analog signal into a digital signal, andnumeral 16 is a demodulation circuit for demodulating the receptionsignal converted into the digital signal and outputting the receptionsignal R. Numeral 17 is a modulation circuit for modulating atransmission signal T, numeral 18 is a D/A converter for converting themodulated transmission signal from a digital signal into an analogsignal, numeral 19 is a band-pass filter for limiting the transmissionsignal converted into the analog signal to a signal of a predeterminedfrequency band, and numeral 20 is an amplifier for amplifying thetransmission signal.

[0113] Operation is hereinafter described. The signals received by thetwo-way transmission antennas 9 a-1 and 9 a-2 for radio communicationare inputted to the level comparator 13 via the duplexers 30-1 and 30-2,the band-pass filters 11-1 and 11-2, and the low-noise amplifiers 12-1and 12-2. The level comparator 13 compares level of the two inputtedsignals (receiving signals), and the antenna switches 14-1 and 14-2 arecontrolled based on the result of the comparison. The reception signalselected by the antenna switch 14-1 passes through the A/D converter 15and the demodulation circuit 16, and is processed by a signal processor(not shown) in a later stage.

[0114] On the other hand, a transmitting signal is inputted to theantenna switch 14-2 via the modulation circuit 17, the D/A converter 18,the band-pass filter 19, and the amplifier 20. As described above, theantenna switch 14-2 is controlled to select the two-way transmissionantenna for radio communication of the higher receiving signal level.Therefore, the transmission signal is transmitted from the two-waytransmission antenna for radio communication of the higher receptionlevel.

[0115] Timing for switching from one of the duplexers 30-1 and 30-2 tothe other is decided on the basis of a transmission-reception switchsignal S to prevent a signal from missing at the moment of switching.Further, timing for switching from one of the antenna switches 14-1 and14-2 for selecting either of the two two-way transmission antennas forradio communication to the other switch is also decided on the basis ofthe transmission-reception switch signal S inputted to the levelcomparator 13.

INDUSTRIAL APPLICABILITY

[0116] The present invention is applicable to installation of ashort-range on-vehicle radio communication system having in-car radiocommunication function in a large-sized vehicle such as bus or train, apassenger car, or a commercial car.

What is claimed is:
 1. A short-range on-vehicle radio communicationsystem having an in-car radio communication function, wherein a two-waytransmission antenna (9 a) for radio communication is arranged outside asheet metal chassis (8 b) of a main body (8).
 2. The short-rangeon-vehicle radio communication system according to claim 1, wherein theshort-range on-vehicle radio communication system is a car navigationunit (8), and the two-way transmission antenna (9 a) for radiocommunication is arranged at a panel portion (8 c) outside the sheetmetal chassis (8 b) of the car navigation unit (8).
 3. The short-rangeon-vehicle radio communication system according to claim 1, wherein thetwo-way transmission antenna (9 a) for radio communication is arrangedoutside the main body (8 a).
 4. The short-range on-vehicle radiocommunication system according to claim 3, wherein the short-rangeon-vehicle radio communication system is a car navigation unit (8 a). 5.The short-range on-vehicle radio communication system according to claim4, wherein a frequency band used in radio communication is a 2.4 GHzband.
 6. The short-range on-vehicle radio communication system accordingto claim 3, wherein the two-way transmission antenna (9 a) for radiocommunication is arranged at a ceiling (A) in a car room.
 7. Theshort-range on-vehicle radio communication system according to claim 6,wherein the two-way transmission antenna (9 a) for radio communicationis arranged in an interior light module (B) on the ceiling in the carroom, on a surface of the module or around the module.
 8. Theshort-range on-vehicle radio communication system according to claim 3,wherein the two-way transmission antenna (9 a) for radio communicationis arranged on a front seat side (C) in the car room.
 9. The short-rangeon-vehicle radio communication system according to claim 8, wherein thetwo-way transmission antenna (9 a) for radio communication is arrangedon a surface of a dashboard in the car room, inside the dashboard oraround the dashboard (D).
 10. The short-range on-vehicle radiocommunication system according to claim 8, wherein the two-waytransmission antenna (9 a) for radio communication is arranged on asurface of either a center console or a floor console in the car room,inside the console or around the console.
 11. The short-range on-vehicleradio communication system according to claim 8, wherein the two-waytransmission antenna (9 a) for radio communication is arranged in thevicinity of a cellular phone holder (2 d) in the car room.
 12. Theshort-range on-vehicle radio communication system according to claim 4,wherein the two-way transmission antenna (9 a) for radio communicationis arranged on a surface of a rear tray in a car room, inside the reartray or around the rear tray (E).
 13. The short-range on-vehicle radiocommunication system according to claim 3, wherein the two-waytransmission antenna (9 a) for radio communication is arranged in atrunk (F) of a vehicle.
 14. The short-range on-vehicle radiocommunication system according to claim 3, wherein the two-waytransmission antenna (9 a) for radio communication is arranged on anouter circumference (G) of the main body.
 15. The short-range on-vehicleradio communication system according to claim 1, wherein plural two-waytransmission antennas (9 a) for radio communication are arranged outsidethe sheet metal chassis (8 b) of the main body (8) in the vehicle. 16.The short-range on-vehicle radio communication system according to claim15, wherein among the plural two-way transmission antennas (9 a) forradio communication, one is arranged at a front portion (D) in thevehicle and another is arranged at a rear portion (H) in the vehicle.17. The short-range on-vehicle radio communication system according toclaim 15, wherein among the plural two-way transmission antennas (9 a)for radio communication, one is arranged at a panel portion (8 c)outside the sheet metal chassis (8 b) and another is arranged outsidethe main body (8 a).
 18. The short-range on-vehicle radio communicationsystem according to claim 15, wherein an antenna output of the highestreception level is selected from the plural two-way transmissionantennas (9 a) for radio communication.
 19. The short-range on-vehicleradio communication system according to claim 15, wherein theshort-range on-vehicle radio communication system is a car navigationunit (8 a).